Employing VLC technology for transmitting data in biological tissue

Abstract. With the development in wireless communication methods, visible light communication (VLC), a subset of Optical Wireless Communication (OWC) has garnered much attention to employ the technology for a secure short-range wireless communication. We present a feasibility study to determine the performance of VLC in short range wireless transmission of data through biological tissue. VLC is a cost efficient and secure means of transmitting high volume of data wirelessly which can considerably reduce the interference issues caused by electromagnetic pulses and external electric fields. We present a simple measurement approach based on Monte Carlo simulation of photon propagation in tissue to estimate the strength of wireless communication with body implant devices. Using light for communication brings inherent security against unauthorized access of digital data which could be acquired from the low energy body implant devices used for medical diagnosis and other studies. This thesis discusses the typical components required to establish VLC such as, transmitter, receiver and the channel mediums. Furthermore, two cases of Monte Carlo simulation of photon-tissue interaction are studied to determine a possibility if VLC is a suitable substitute to radio frequency (RF) for a more wireless communication with the body implants. The process of theoretical measurement begins with conversion of light intensity into an electrical signal and an estimation of achievable data rate through a complex heterogeneous biological tissue model. The theoretically achieved data rates of the communication were found to be in the order of megabits per second (Mbps), ensuring a possibility to utilize this technology for short range reliable wireless communication with a wider range and application of implant medical devices. Biophotonics.fi presents a computational simulation of light propagation in different types of computational tissue models comprehensively validated by comparison with the team’s practical implementation of the same setup. This simulation is also used in this thesis (5.2.2) to approximate more accurate data rates of communication in case of a practical implementation

A review of gallium nitride LEDs for multi-gigabit-per-second visible light data communications

The field of visible light communications (VLC) has gained significant interest over the last decade, in both fibre and free-space embodiments. In fibre systems, the availability of low cost plastic optical fibre (POF) that is compatible with visible data communications has been a key enabler. In free-space applications, the availability of hundreds of THz of the unregulated spectrum makes VLC attractive for wireless communications. This paper provides an overview of the recent developments in VLC systems based on gallium nitride (GaN) light-emitting diodes (LEDs), covering aspects from sources to systems. The state-of-the-art technology enabling bandwidth of GaN LEDs in the range of >400 MHz is explored. Furthermore, advances in key technologies, including advanced modulation, equalisation, and multiplexing that have enabled free-space VLC data rates beyond 10 Gb/s are also outlined

AI/ML assisted Li-Fi communication systems for the future 6G communication systems

Η πανταχού παρούσα εξάπλωση της ασύρματης σύνδεσης κατά την τελευταία δεκαετία είχε ως αποτέλεσμα μια τεράστια αύξηση του όγκου της κίνησης και μια τεράστια ζήτηση, η οποία δημιούργησε μια αξιοσημείωτη πίεση στους πόρους του δικτύου που δεν μπορούν να διαχειριστούν εξαρχής λόγω της σπανιότητας του εύρους ζώνης. Επομένως; Η Optical Wireless Communication θεωρείται ως η αναδυόμενη λύση για τα τρέχοντα δίκτυα ραδιοφώνου, όπου λειτουργεί στην εκμετάλλευση του φωτός ως ασύρματος φορέας και έχει ταξινομηθεί ως φιλική προς το περιβάλλον τεχνολογία λόγω της βιωσιμότητας και του επιπέδου ασφάλειας. Το Light-Fidelity (LiFi) είναι το πιο πρόσφατο παράδειγμα της οπτικής ασύρματης επικοινωνίας όπου υπάρχουν νέα χαρακτηριστικά όπως π. Στο σύστημα έχουν εισαχθεί τεχνικές διαμόρφωσης πολλαπλών φορέων και τεχνολογίες πολλαπλής πρόσβασης. Αυτή η αναφορά παρουσιάζει τη διαδικασία σχεδιασμού ενός πομποδέκτη LiFi που χρησιμοποιεί το MATLAB. όπου όλα τα μέρη του συστήματος προσομοιώθηκαν για να μιμηθούν ένα σύστημα LiFi σε ένα εσωτερικό περιβάλλον που είναι ένα δωμάτιο με διαστάσεις 5 x 5 x 3 m. Ο πομποδέκτης έχει χαρακτηριστεί με χρήση οπτοηλεκτρονικών συσκευών περοβσκίτη λόγω της πολλά υποσχόμενης απόδοσής του όσον αφορά την εκπομπή φωτός και την ανίχνευση. Ωστόσο, έχει προκύψει σημαντικός όγκος θορύβου λόγω της φωτοανίχνευσης που έχει μετριαστεί με την εισαγωγή ενός ενισχυτή transimpedance μετά τον φωτοανιχνευτή και την εφαρμογή ενός μηχανισμού εκτίμησης καναλιών στην πλευρά του δέκτη. Τα ληφθέντα αποτελέσματα έδειξαν ότι το σχεδιασμένο σύστημα μπορεί να επιτύχει περίπου 3,5 Mbps με 25dB SNR και λιγότερο από 4x10^(-6) BER χρησιμοποιώντας 5 πομπούς με 1000 LED σε κάθε πομπό, χωρίς να λαμβάνεται υπόψη καμία εξωτερική πηγή θορύβου όπως ο θόρυβος περιβάλλοντος. Οι πιθανοί περιορισμοί για ένα τέτοιο σύστημα είναι οι προδιαγραφές των οπτοηλεκτρονικών συσκευών που περιλαμβάνουν, την επιφάνεια της συσκευής, το οπτικό πεδίο του φωτοανιχνευτή και τη γωνία μισής ισχύος του LED. Ωστόσο, τα συστήματα οπτικών ασύρματων επικοινωνιών είναι πιο ευέλικτα για βελτιστοποίηση και τα σχέδια μπορούν να τυποποιηθούν σύμφωνα με την ζητούμενη υπηρεσία και τη φύση του περιβάλλοντος λόγω της ποικιλίας των διαθέσιμων συσκευών με χαμηλό κόστος.The ubiquitous spread of the wireless connection during the last decade has resulted in a tremendous growth in the traffic volume and a huge demand, which created a remarkable pressure on the network’s resources that can’t be managed due to bandwidth scarcity in the first place. Therefore; Optical Wireless Communication is considered as the emerging solution for the current radio networks, where it works on exploiting light as a wireless carrier and it has been classified as eco-friendly technology due to its sustainability and safety level. Light-Fidelity (LiFi) is the most recent paradigm of the optical wireless communication where new features such as; multicarrier modulation techniques and multiple access technologies have been introduced to the system. This report presents the design process of a LiFi transceiver using MATLAB; where all system parts were simulated to imitate a LiFi system in an indoor environment which is a room with dimensions of 5 x 5 x 3m. The transceiver has been characterised using perovskite optoelectronic devices due to its promising performance in terms of light emission and detection. However, a considerable amount of noise has been resulted due to the photodetection that has been mitigated using inserting a transimpedance amplifier after the photodetector and implement a channel estimation mechanism at the receiver side. The obtained results have demonstrated that the designed system can achieve around 3.5Mbps with 25dB SNR and less then 4x10^(-6) BER using 5 transmitters with 1000 LED at each transmitter, without considering any external source of noise such as the ambient noise. The prospective limitations for such a system are the optoelectronic devices specs which include, the device’s surface area, the photodetector’s field of view, and the half power angle of the LED. However, the optical wireless communication systems are more flexible to be optimized and the designs can be standardized according to the requested service and the environment nature due to the variety of the available devices with low cost

Spectrum and energy efficient digital modulation techniques for practical visible light communication systems

The growth in mobile data traffic is rapidly increasing in an unsustainable direction given the radio frequency (RF) spectrum limits. Visible light communication (VLC) offers a lucrative solution based on an alternative license-free frequency band that is safe to use and inexpensive to utilize. Improving the spectral and energy efficiency of intensity modulation and direct detection (IM/DD) systems is still an on-going challenge in VLC. The energy efficiency of inherently unipolar modulation techniques such as pulse-amplitude modulation discrete multitone modulation (PAM-DMT) and asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) degrades at high spectral efficiency. Two novel superposition modulation techniques are proposed in this thesis based on PAM-DMT and ACO-OFDM. In addition, a practical solution based on the computationally efficient augmented spectral efficiency discrete multi-tone (ASE-DMT) is proposed. The system performance of the proposed superposition modulation techniques offers significant electrical and optical power savings with up to 8 dB in the electrical signal-to-noise ratio (SNR) when compared with DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM). The theoretical bit error ratio (BER) performance bounds for all of the proposed modulation techniques are in agreement with the Monte-Carlo simulation results. The proposed superposition modulation techniques are promising candidates for spectrum and energy efficient IM/DD systems. Two experimental studies are presented for a VLC system based on DCO-OFDM with adaptive bit and energy loading. Micrometer-sized Gallium Nitride light emitting diode (m-LED) and light amplification by stimulated emission of radiation diode (LD) are used in these studies due to their high modulation bandwidth. Record data rates are achieved with a BER below the forward error correction (FEC) threshold at 7.91 Gb/s using the violet m-LED and at 15 Gb/s using the blue LD. These results highlight the potential of VLC systems in practical high speed communication solutions. An additional experimental study is demonstrated for the proposed superposition modulation techniques based on ASE-DMT. The experimentally achieved results confirm the theoretical and simulation based performance predictions of ASE-DMT. A significant gain of up to 17.33 dB in SNR is demonstrated at a low direct current (DC) bias. Finally, the perception that VLC systems cannot work under the presence of sunlight is addressed in this thesis. A complete framework is presented to evaluate the performance of VLC systems in the presence of solar irradiance at any given location and time. The effect of sunlight is investigated in terms of the degradations in SNR, data rate and BER. A reliable high speed communication system is achieved under the sunlight effect. An optical bandpass blue filter is shown to compensate for half of the reduced data rate in the presence of sunlight. This thesis demonstrates data rates above 1 Gb/s for a practical VLC link under strong solar illuminance measured at 50350 lux in clear weather conditions

Physical Layer Techniques for Indoor Wireless Visible Light Communications

The growing demand for bandwidth-hungry applications and increasing number of smart interconnected devices has increased the data traffic on radio access networks. Subsequently, the saturating spectral efficiencies in crowded radio frequency spectrum has impelled the researchers to exploit the optical spectrum for communications. In particular, many developments in the visible light communication (VLC) as a combined lighting and communications system have taken place. Despite abundant optical bandwidth, the data transmission rates and power efficiencies in VLC are partly limited by the electrical channel bandwidth and the type of signalling sets which can be used in this intensity modulated, direct detected system. In order to improve the power and spectral efficiencies, this thesis focuses on physical layer (PHY) techniques. The state-of-the-art single channel modulations (SCM) based on M-PAM, multi-channel modulations (MCM) based on OFDM, and IEEE standardised multi-colour modulations are investigated comprehensively through simulations and theoretical analysis, over representative VLC channels considering the optical properties of front-end devices. The bit error performances and spectral efficiencies of DC-biased and non DC-biased MCM systems are compared. A new vector coding based MCM is proposed to optimally utilise the channel state information at the transmitter as an alternative to optical OFDM. The throughputs, peak-to-average power ratios and DC-bias requirements of SCM and MCM systems are investigated which show that the lower DC-bias requirements reduce power consumed for the same throughput in SCM systems when compared to MCM systems. A new quad-chromatic colour shift keying (CSK) system is proposed which reduces power requirements and complexity, enhances throughput and realises a four-dimensional signalling to outperform the IEEE standardised tri-chromatic CSK system. For improved power efficiency and throughput of VLC PHY, use of rate-adaptive binary convolutional coding and Viterbi decoding is proposed along with frequency domain channel equalisation to mitigate temporal dispersion over representative VLC channels

Améliorations des transmissions VLC (Visible Light Communication) sous contrainte d'éclairage : études théoriques et expérimentations

Abstract : Indoor visible light communication (VLC) networks based on light-emitting diodes (LEDs) currently enjoy growing interest thanks in part to their robustness against interference, wide license-free available bandwidth, low cost, good energy efficiency and compatibility with existing lighting infrastructure. In this thesis, we investigate spectral-efficient modulation techniques for the physical layer of VLC to increase throughput while considering the quality of illumination as well as implementation costs. Numerical and experimental studies are performed employing pulse amplitude modulation (PAM) and carrierless amplitude and phase (CAP) modulation under illumination constraints and for high modulation orders. Furthermore, the impact of LED nonlinearity is investigated and a postdistortion technique is evaluated to compensate these nonlinear effects. Within this framework, transmission rates in the order of a few hundred Mb/s are achieved using a test bench made of low-cost components. In addition, an imaging multiple input multiple-output (MIMO) system is developed and the impact on performance of imaging lens misalignment is theoretically and numerically assessed. Finally, a polynomial matrix decomposition technique based on the classical LU factorization method is studied and applied for the first time to MIMO VLC systems in large space indoor environments.Les réseaux de communication en lumière visible (VLC) s’appuyant sur l’utilisation de diodes électroluminescentes (LED) bénéficient actuellement d’un intérêt grandissant, en partie grâce à leur robustesse face aux interférences électromagnétiques, leur large bande disponible non-régulée, leur faible coût, leur bonne efficacité énergétique, ainsi que leur compatibilité avec les infrastructures d’éclairage déjà existantes. Dans cette thèse, nous étudions des techniques de modulation à haute efficacité spectrale pour la couche physique des VLC pour augmenter les débits tout en considérant la qualité de l’éclairage ainsi que les coûts d’implémentation. Des études numériques et expérimentales sont réalisées sur la modulation d’impulsion d’amplitude (PAM) et sur la modulation d’amplitude et de phase sans porteuse (CAP) sous des contraintes d’éclairage et pour des grands ordres de modulation. De plus, l’impact des non-linéarités de la LED est étudié et une technique de post-distorsion est évaluée pour corriger ces effets non-linéaires. Dans ce cadre, des débits de plusieurs centaines de Mb/s sont atteints en utilisant un banc de test réalisé à partir de composants à bas coûts. Par ailleurs, un système multi-entrées multi-sorties (MIMO) imageant est également développé et l’impact du désaxage de l’imageur sur les performances est étudié. Finalement, une technique de décomposition polynomiale basée sur la méthode de factorisation classique LU est étudiée et appliquée aux systèmes MIMO VLC dans des grands espaces intérieurs

Power and spectrally efficient integrated high-speed LED drivers for visible light communication

Recent trends in mobile broadband indicates that the available radio frequency (RF) spectrum will not be enough to support the data requirements of the immediate future. Visible light communication, which uses visible spectrum to transmit wirelessly could be a potential solution to the RF ’Spectrum Crunch’. Thus there is growing interest all over the world in this domain with support from both academia and industry. Visible light communication( VLC) systems make use of light emitting diodes (LEDs), which are semiconductor light sources to transmit information. A number of demonstrators at different data capacity and link distances has been reported in this area. One of the key problems holding this technology from taking off is the unavailability of power efficient, miniature LED drive schemes. Reported demonstrators, mostly using either off the shelf components or arbitrary waveform generators (AWGs) to drive the LEDs have only started to address this problem by adopting integrated drivers designed for driving lighting installations for communications. The voltage regulator based drive schemes provide high power efficiency (> 90 %) but it is difficult to realise the fast switching required to achieve the Mbps or Gbps data rates needed for modern wireless communication devices. In this work, we are exploiting CMOS technology to realise an integrated LED driver for VLC. Instead of using conventional drive schemes (digital to analogue converter (DAC) + power amplifier or voltage regulators), we realised a current steering DAC based LED driver operating at high currents and sampling rates whilst maintaining power efficiency. Compared to a commercial AWG or discrete LED driver, circuit realised utilisng complementary metal oxide semiconductor (CMOS) technology has resulted in area reduction (29mm2). We realised for the first time a multi-channel CMOS LED driver capable of operating up to a 500 MHz sample rate at an output current of 255 mA per channel and >70% power efficiency. We were able to demonstrate the flexibility of the driver by employing it to realise VLC links using micro LEDs and commercial LEDs. Data rates up to 1 Gbps were achieved using this system employing a multiple input, multiple output (MIMO) scheme. We also demonstrated the wavelength division multiplexing ability of the driver using a red/green/blue commercial LED. The first integrated digital to light converter (DLC), where depending on the input code, a proportional number of LEDs are turned ON, realising a data converter in the optical domain, is also an output from this research. In addition, we propose a differential optical drive scheme where two output branches of a current DAC are used to drive two LEDs achieving higher link performance and power efficiency compared to single LED drive

Improved Visible Light Communication Receiver Performance by Leveraging the Spatial Dimension

In wireless communications systems, signals can be transmitted as time (temporal) or spatial variants across 3D space, and in both ways. However, using temporal variant communication channels in high-speed data transmission introduces inter-symbol interference (ISI) which makes the systems unreliable. On the other hand, spatial diversity in signal processing reduces the ISI and improves the system throughput or performance by allowing more signals from different spatial locations at the same time. Therefore, the spatial features or properties of visible light signals can be very useful in designing a reliable visible light communication (VLC) system with higher system throughput and making it more robust against ambient noise and interference. By allowing only the signals of interest, spatial separability in VLC can minimize the noise to a greater extent to improve signal-to-noise ratio (SNR) which can ensure higher data rates (in the order of Gbps-Tbps) in VLC. So, designing a VLC system with spatial diversity is an exciting area to explore and might set the foundation for future VLC system architectures and enable different VLC based applications such as vehicular VLC, multi-VLC, localization, and detection using VLC, etc. This thesis work is motivated by the fundamental challenges in reusing spatial information in VLC systems to increase the system throughput or gain through novel system designing and their prototype implementations

Visible Light Communication (VLC)

Visible light communication (VLC) using light-emitting diodes (LEDs) or laser diodes (LDs) has been envisioned as one of the key enabling technologies for 6G and Internet of Things (IoT) systems, owing to its appealing advantages, including abundant and unregulated spectrum resources, no electromagnetic interference (EMI) radiation and high security. However, despite its many advantages, VLC faces several technical challenges, such as the limited bandwidth and severe nonlinearity of opto-electronic devices, link blockage and user mobility. Therefore, significant efforts are needed from the global VLC community to develop VLC technology further. This Special Issue, “Visible Light Communication (VLC)”, provides an opportunity for global researchers to share their new ideas and cutting-edge techniques to address the above-mentioned challenges. The 16 papers published in this Special Issue represent the fascinating progress of VLC in various contexts, including general indoor and underwater scenarios, and the emerging application of machine learning/artificial intelligence (ML/AI) techniques in VLC